Investments - Additional Information (Detail) (USD $)	6 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Level 3 Proportion to fixed maturities and equity securities	0.60%	0.40%
Other-than-temporary impairments		$ 20,000
Other-than-temporary impairments, after tax		13,000
Total issues of fixed-maturities and equities	1,360	1,373
Balances related to bifurcated credit loss positions included in other comprehensive income	$ 22,000,000	$ 22,000,000

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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